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On 9 February 2015, the European Physical Society [EPS], the Nederlandse Natuurkundige Vereniging – the Netherlands Physical Society [NNV] and the University of Leiden unveiled a plaque commemorating the former location of the Kamerlingh Onnes Laboratory and the Instituut-Lorentz as an EPS Historic Site. A series of talks preceded the unveiling ceremony, presided by Johannes Maria van Ruitenbeek, the President of the NNV.

Dirk van Delft, the Director of the Boerhaave Science Museum in Leiden gave an overview of the life work of Professor Kamerlingh Onnes, as well as the achievements of the University of Leiden. Carlo Beenakker from the Lorentz Institute provided an historical perspective of the building of the Kamerlingh Onnes Laboratory. Finally, Christophe Rossel, EPS President-elect, gave an overview of the EPS Historic Site programme.

The descendants of Professor Kamerlingh Onnes also attended, along with around 50 other participants from the surrounding scientific community. Following the talks, the participants walked to the site of the Kamerlingh Onnes Laboratory (which is now the University of Leiden Law Faculty).

A very impressive bronze plaque in front of the building reads:

European Physical Society – EPS Historic Site

Kamerlingh Onnes Laboratory and Lorentz Institute

Here, in 1908, Heike Kamerlingh Onnes first succeeded in liquefying helium. This opened up a wide field of low-temperature experiments, and led to the discovery of superconductivity in 1911. Here, in 1896, Pieter Zeeman discovered the splitting of atomic spectral lines by a magnetic field. Hendrik Lorentz interpreted this as an effect of the magnetic force on the oscillation of hypothetical charged particles, which later became known as electrons.

In order to commemorate the important discoveries in physics that were made on this site, the President-Elect of the EPS, Dr. Christophe Rossel, will unveil a plaque that will be placed at the entrance of the current Kamerlingh Onnes building (Steenschuur 25, Leiden).